The invention relates to a method of manufacturing a cathode ray tube, which tube comprises an envelope portion having a longitudinal axis and a gun assembly having a longitudinal axis, in which
a. the envelope portion is fixed in an assembly device in a given position, PA0 b. the gun assembly is provided in the envelope portion, the said axes substantially coinciding, PA0 c. the location and/or the angle orientation of the gun assembly is adjusted with respect to the axis of the envelope portion and portion; PA0 d. the gun assembly is secured in the envelope.
Such a cathode ray tube may be a television camera tube or a display tube. Display tubes have a wide field of application. They are used, for example, as projection television display tubes, oscilloscope tubes, colour display tubes and DGD-tubes (DGD=Data Graphic Display). All these types of tube comprise an electron gun system for generating at least one electron beam. This electron beam must enter the deflection fields in a precise manner and must land at a precise location on a target, such as a display screen, in the tube. A very accurate assembly of the electron gun system in the envelope during the manufacture of the tube is therefore necessary.
Such a method is known from U.S. Pat. No. 3,807,006 in which the assembly is described of a gun assembly in the envelope of a colour display tube. The mechanical adjustment preceding the assembly as described in the patent is not sufficiently accurate. When providing the gun assembly in the tube neck, the accurate adjustment is often lost. Therefore, French Patent Application No. 7704772 (corresponding to British Patent Application 1,560,199) describes an optical alignment of the gun assembly in the tube neck. For that purpose, gun electrodes must be provided with extra apertures through which, during the adjustment, a light beam passes which is then detected. A disadvantage of this method is that, during the adjustment, the light beam passes two times through an often curved part of the envelope, as a result of which errors are introduced.